High power electrical/electronic circuitries can generate substantial amounts of heat during operation, causing overheating that can damage the circuitries, or deteriorate their reliability, if proper cooling and/or heatsinking is not applied. For example, high power amplifiers (HPA) used for beaming microwave bursts e.g., as used in satellite communication and radar systems, can experience very high power activation bursts resulting in abrupt heating of the amplifying circuitries. Conventionally, fluid-cooled (e.g., by air or water) heatsinks (e.g., plate/fin/conduction path radiators) are thermally coupled to the packaging of the HPA circuitries to dissipate and distribute the heat thereby produced. However, electronic circuitries are becoming compactly smaller and more powerful, thus yielding highly concentrated heat sources formed by the high power circuitries, which aggravates the cooling problem, particularly under the growing demand for dense packaging, low weight, and operation in harsh environments.
The conventional fluid cooled heatsink solutions can be effective in applications wherein the produced heat is uniformly distributed across the top surface of the semiconductor die. However, as the electronic components are diminished in size, the conventional fluid cooled heatsink solutions are becoming less effective, since the significant amounts of the heat is produced in small discrete areas of the IC densely populated by the high-power circuitries, resulting in significantly high temperatures evolving in small discrete areas of the IC substrate. Since the high heat producing spots are discretely distributed over the area of the IC substrate, only small amounts of heat can be dispersed by the fins at the extremities (away from the heat source) of the heatsink, such that standard heatsinks cannot effectively cool the IC.
A possible attempt to overcome this problem suggests spreading the heat more efficiently through the base of the heatsink. For example, in some of the solutions used nowadays heat pipes (also known as vapor chambers) are embedded in the heatsink to improve heat dispersion from the condensed high-power circuitry areas to the extremities. Though heat pipe techniques can somewhat mitigate problems associated with distribution of heat in heatsink devices, they are not so effective when excess amounts of heat needs to be quickly removed from discrete locations on a surface of a high frequency IC (>1 GHz).
For example, temperature control is critical to the performance of radar systems, since the electrical performance of the HPAs decreases as their temperatures are increased. Hence, radar system are typically required to maintain the temperatures of the HPAs junctions below about 150° C., and guarantee that the temperature variations between the modules do not exceed approximately 10° C., to assure reliability. These requirements can be theoretically achieved by reducing the duty cycle, and/or the pulse width, of the radar system, and/or using powerful cooling equipment, which is inevitably costly in terms of weight, size, and monetary price, and usually not so reliable. In practice, radar systems nowadays require some combination/tradeoff of these temperature control schemes to guarantee continuous reliable operation.
Some heatsink/cooling techniques knows from the patent literature are briefly described hereinbelow:
U.S. Pat. No. 6,848,500 discloses an apparatus for reducing peak temperatures and thermal excursions, of semiconductor devices, particularly in pulsed power applications. The apparatus comprises thermally coupling phase change material (PCM) to the dissipating semiconductor device. PCM absorbs heat and stays at a constant temperature during its phase change from solid to liquid. The PCM melting point is chosen so that it is just below the temperature the device would otherwise achieve. When the device approaches the maximum temperature, the PCM melts, drawing heat from the device and lowering the device's peak temperature. As the device stops dissipating, after its pulse period, the PCM material solidifies releasing the heat it absorbed. The apparatus lowers the peak temperature by absorbing heat when the device is dissipating. The apparatus also keeps the semiconductor device from cooling off as much as it would cool without the apparatus, as the PCM material releases heat during the part of the cycle when it is re-solidifying, i.e., when the pulse power is off. By lowering the peak temperature the device achieves, and increasing the temperature of the device when it is in the off portion of its pulsed power cycle the temperature excursions of the device during operation are reduced. By reducing the temperature swings, that the device sees during operation, the thermal stress is reduced and the reliability of the device is improved.
US Patent Publication No. 2002/033247 describes a device comprising a phase change material arranged in or on a heat sink element in such a way that significant heat flow from a central processing unit (CPU) via a support only if the heat sink exceeds the phase change temperature of the phase change material, which thus ensures that the phase change material only absorbs the output peaks from the CPU.
International Patent Publication No. WO 2004/109798 describes a method for thermally protecting electronic units in an electronic device, particularly in a mobile radio device, with heat-generating electrical units (heat sources), particularly with electrical components and circuits. According to the invention, the heat-generating electrical units are brought into working contact with a substance system (heat sink), which has a phase-change temperature that is near a predetermined operating temperature of the electronic device.